This invention relates to a wheel angular acceleration sensor for vehicle anti-lock controllers. More specifically, the invention relates to an improved form of wheel angular acceleration sensor which comprises an output shaft coupled to, and rotating with, the wheel that is braked by the wheel brake; a flywheel rotatably mounted and axially displaceable on the output shaft; a clutch means disposed between the output shaft and the flywheel and adapted to transmit the driving torque of the output shaft to the flywheel under normal operating conditions and, when the vehicle wheel approaches a locked condition during braking, to allow the flywheel to overrun the output shaft; and a cam mechanism cooperable with the clutch means between the output shaft and the flywheel to give the flywheel an axial displacement in response to the overrunning rotation of the flywheel, the axial displacement of the flywheel being operative in the control of the braking of the vehicle wheel.
Wheel angular acceleration sensors of the involved type are known, one such sensor device being described in Japanese Laid-Open Publication No. 126241/1983. In such conventional wheel angular acceleration sensors, the flywheel is directly rotatably and axially slidably supported on the output shaft and, thus, is subject to friction resistance between it and the output shaft. Further, the friction resistance varies even with small changes in the lubricated condition of the organization, such that it is difficult to stabilize the axial displacement characteristics of the flywheel with respect to the thrust force produced by the cam mechanism.
The present invention seeks to overcome the above problem and has as a principal object to provide a wheel angular acceleration sensor within which the flywheel is supported with respect to the output shaft without any physical contact occurring between the flywheel and the output shaft to obtain stable axial displacement characteristics of the flywheel.